Systems and methods for generating damped electromagnetically actuated planar motion for audio-frequency vibrations

ABSTRACT

A vibration module for applying vibrational tractions to a wearer&#39;s skin is presented. Use of the vibration module in headphones is illustrated for providing tactile sensations of low frequency for music, for massage, and for electrical recording and stimulation of the wearer. Damped, planar, electromagnetically-actuated vibration modules of the moving magnet type are presented in theory and reduced to practice, and shown to provide a substantially uniform frequency response over the range 40-200 Hz with a minimum of unwanted audio.

CROSS-REFERENCE TO RELATED APPLICATIONS

Any and all applications for which a foreign or domestic priority claimis identified in the Application Data Sheet as filed with the presentapplication are hereby incorporated by reference under 37 CFR 1.57.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to tactile transducers that produce bassfrequency vibrations for perception by touch.

Description of the Related Art

Below about 200 Hz, the lower the frequency of sound, the more it isperceived not only by vibration of the ear drum but also by touchreceptors in the skin. This sensation is familiar to anyone who has“felt the beat” of strong dance music in the chest, or through the seatof a chair, or has simply rested a hand on a piano. The natural stimulusis both auditory and tactile, and a true reproduction of it is possibleonly when mechanical vibration of the skin accompanies the acousticwaves transmitted through the air to the ear drum.

The prior art in audio-frequency tactile transducers primarily employaxial shakers. FIG. 1 shows an exploded view of a prior art headphoneset 10 that includes axial shaker 100, including moving mass 114suspended on spiral-cut spring 112, stator 116, and voice coil 118. Theconstruction of such axial shakers mimics conventional audio drivers inwhich the light paper cone is replaced with a heavier mass, and a morerobust suspension is provided, typically a spiral-cut metal spring.

A drawback of this construction is the production of unwanted acousticnoise. This occurs because the axial shaker is mounted in the headphoneear cup with the motion axis pointed at the opening of the ear canal.FIG. 2A shows a perspective view of prior art headphone set 20 thatincludes an axial shaker that vibrates along the z-axis and stimulatesthe skin by plunging the ear cup against the side of the user's head.Axial movement of the mass causes a countermovement of the entire earcup itself, which is typically sealed over the pinna. Thus, the sameforce that stimulates the skin under the ear cup cushions unfortunatelyalso plunges air into the listener's ear canal, overwhelming the outputof the audio driver and generating the excess unwanted acoustic noise.

FIG. 2B shows a graph illustrating the excess apparent bass audiogenerated by the prior art headphones of FIG. 2A. In particular, FIG. 2Billustrates that the relatively flat acoustic frequency response of theheadphones alone (traces labeled “off”) is degraded when the inertialshaker is turned on to progressively stronger levels (traces labeled“on”). In this example, significant audio is added to the acousticfrequency response, causing an undesirable bump of 10-20 dB in the50-100 Hz range. The result is a bass-heavy sound in which upperfrequencies are underrepresented, and the user's perception is one ofmuffled, muddy sound.

The problem of uneven frequency response is typically made worse by alack of mechanical damping. Leaving the system underdamped means thatsteady state signals near mechanical resonance achieve high amplitude,leading to a peaked response, and that the system rings after excitationis stopped, further degrading audio fidelity. Such a bump is evident inthe frequency response of the prior art (FIG. 2B), where actuating thetactile transducer increases the acoustic output of the headphone 10 to20 dB above the 90 dB Sound Pressure level that is indicated by the “0”reference line.

Another approach in the prior art, also problematic, is the use ofun-damped eccentric rotating motors (“ERMs”) and un-damped linearresonant actuators (“LRAs”). Small, un-damped ERMs are incompatible withhigh-fidelity audio for a few reasons. First, it generally takes about20 milliseconds to “spin up” an ERM to a frequency that produces anacceleration large enough to be felt. By then an impulse signal (forexample, the attack of a kick drum) will have passed. Second, in an ERMthe acceleration, which can be likened to a “tactile volume,” andfrequency, which can be likened to a “tactile pitch” are linked andcannot be varied independently. This linkage is fundamentallyincompatible with acoustic fidelity.

The main drawback of LRAs is the dependence on the “resonance,” that thename suggests. The devices are designed for tactile alerts, notfidelity, and so they resonate at a single frequency and produceperceptible vibration at only that frequency. For example a typical LRAmight produce up to 1.5 g of acceleration at 175±10 Hz, but less than0.05 g outside this 20 Hz range. Such a high Q-factor renders this sortof device useless for high fidelity reproduction of low frequencytactile effects in the 15-120 Hz range. Despite these problems, LRAshave been contemplated for vertical mounting in the top cushion of aheadphone bow.

In addition to the limited frequency range of LRAs there is a anotherproblem with using LRAs as audio-frequency tactile transducers is that atransducer mounted vertically between the headphone bow and the top ofthe skull flexes the bow. At a fine scale, this flexion makes the bowflap like the wings of a bird, where an ear cup is situated at each wingtip. The inward-outward component of the flapping plunges the ear cupsagainst the sides of the wearer's head, again producing undesirableaudio that competes with and distorts the acoustic response of the audiodrivers in the ear cups.

To avoid such unwanted audio, one approach is to construct alow-profile, vibrating module which moves a mass in-plane (i.e. in thex-y plane of FIG. 2A). This approach minimizes the surface area that isoriented to cause the problematic axially directed acoustic radiation.When mounted in an ear cup, such an in-plane vibrating module producesmotion parallel with the surface of the side of the head. This movementeffectively shears the skin, creating tactile sensation with littleeffect on the volume of air trapped between the ear cup and the eardrum. Acoustic noise is therefore minimized. Consider the differencebetween sliding a glass over a table top (planar motion of the presentinvention) and plunging a toilet (axial motion, as used in prior art).Although this in-plane approach has been contemplated, the dielectricelastomer actuators proposed for this purpose are expensive and complexdevices that require high voltage electronics. Another drawback of thisapproach was that no provision was made for critically damping thosetransducers. Accordingly the tactile acceleration frequency response wasunderdamped, with a claimed Q-factor of 1.5 to 3.

In terms of electromagnetic actuation, a relatively thin, flatarrangement of a coil and two magnets that produces planar motion hasbeen disclosed. In particular, the vibration module includes asingle-phased electromagnetic actuator with a movable member comprisedof two parallel thin magnets magnetized transversely in oppositedirections and connected by a magnet bracket, and a means for guidingthe magnet bracket.

Although this general approach to providing electromagnetic actuationhas not been applied in headphones, it has been applied to the problemof providing hap tic feedback in computer input devices like joysticks.One such device includes an actuator comprising a core member having acentral projection, a coil wrapped around the central projection, amagnet positioned to provide a gap between the core member and themagnet, and a flexible member attached to the core member and themagnet. In this design, the motion is guided by a parallel pair offlexures.

A drawback of this guiding approach is the vulnerability of flexures tobuckling when loaded by longitudinal compression. Compressivelongitudinal loads on the flexures arise naturally from the attractionof the magnet pair riding the flexures to iron flux guides on the coilside, such as the E-core that provides the central projection supportingthe coil. Accordingly, the flexures must be thick enough to resist thisload without Euler buckling. This thickness comes at the expense ofincreased stiffness in the motion direction, which may undesirablyimpede movement.

Despite this drawback, the general approach has been applied elsewhere.For example, a flexure-guided surface carrying the magnets has beencontemplated for use as the face of a massaging element. One approach tomitigating the buckling problem is to bear the compressive load on anelastic element such as foam. Supporting the load with an elasticelement has some undesirable drawbacks, however. The foam adds stiffnessin the direction of travel, and may significantly increase the thicknessof the assembly, since the foam layer must be thick enough that themaximum shear strain (typically <100%) allows adequate travel.

An alternative approach to suspending a moving element arranges the longaxis of the flexures in the plane of a substantially flat transducer.Because slender flexures resist transverse shear loads more effectivelythan longitudinal compressive loads, thinner flexures may be used,providing less impediment to motion.

Therefore, there exists a need for novel audio-frequency tactiletransducers and devices.

SUMMARY OF THE DISCLOSURE

In some embodiments, proposed herein is a thin, flat vibration modulewith a movable member that is electromagnetically actuated to producemotion in-plane. Motion of the movable member can be damped so that thesteady-state sinusoidal voltages applied to the module at differentfrequencies produce an acceleration response of the movable member thatis substantially uniform over the range of 40-200 Hz. The module can bemounted in a headphone so that the motion axis lies substantiallyparallel to the sagittal plane of the wearer's head, so that the motiondoes not plunge the ear cup toward the wearer's ear canal, whichproduces unwanted audio and/or distortions.

In some embodiments, the module may consist of a mass and thin magnets,polarized through their thickness, where the mass and magnets aremovably suspended inside a housing. The suspension may include flexures,bushings, ball bearings, or a ferrofluid layer, for example. The housingmay include one or more conductive coils that carry electrical currentused to vibrate the movable portion. To facilitate mounting of themodule in the ear cup of a headphone, the geometry of the mass, coil,and housing may be substantially planar, (e.g. with a thickness lessthan one-third the length or width). The vibration of the moving portionmay be damped using a suitable approach, such as the shearing of a layerof ferrofluid, oil, grease, gel, or foam, or the passage of air throughan orifice, for example.

In some embodiments, flexures suspending the mass and magnets can bemolded into the housing. In yet another embodiment, flexures may havetabs that engage receiving holes in the housing.

In some embodiments, the mass may have a central pocket that providesspace for the magnets and coil. In other embodiments, the mass may lieadjacent to the magnets. In still other embodiments, the mass may be abattery for powering the module.

In some embodiments, the flexures can extend radially from a central hubto guide torsional rotation of the magnets and mass. Mounted in an earcup in a plane parallel with the wearer's sagittal plane, theseembodiments produce torsional rotation of the ear cup cushion againstthe wearer's skin. Multiple magnets and coils may be used in place of asingle electromagnetic element.

In some embodiments, the module may be made of compliant materialssuitable for direct skin contact. The skin-facing portion of the housingmay be comprised of a stretchable cover. The magnets underneath thiscover may be embedded in a puck comprised of compliant elastomer. Thepuck may be suspended on a layer of ferrofluid. The upper cover may besealed at the perimeter to a lower cover to provide an impermeablecompliant housing that holds the puck and ferrofluid in proximity to acoil. The underlying coil itself may be embedded in a compliantelastomeric material so that the entire module is compliant.

Planar motion of the module may be provided by various arrangements ofmagnets and coils. In some embodiments, a mass may be urged laterally bya magnet that is polarized along the axis of motion. To reduce themodule's thickness, the lateral dimension of the magnet may beelongated, fitted with flux guides, and may be driven by an elongatedoval coil that operates within an air gap defined by the flux guide. Inother embodiments, the mass may be urged laterally by several magnetspolarized along the motion axis, arranged side-by-side, and situated onthe one edge of the mass. In still other embodiments, a long thin magnetpolarized through the thickness direction may lie within a coil.Movement of the magnet within the coil may be coupled to the mass bybrackets, and the motion of the magnet within the tube may be guided byferrofluid bearing.

In some embodiments, the module can be provided with a clear plate thatenables viewing of the motion within it. The module may be mounted in anear cup with a window that provides a view of the motion inside themodule. The ear cup may include a retaining element for the module.

In some embodiments, the complaint module may be integrated directlyinto cushions on the headphone bow, so as to apply vibratory sheartractions to the skin. In other embodiments, one or more of the modulesmay be mounted on movable armatures fixed to the ear cup and or bow ofthe headphones. The armatures may include rotational and prismaticdegrees of freedom, and may be spring loaded to oppose the module to theskin, and may also be electromechanically actuated to produce amassaging motion on the skin of the scalp or face. The armature mayinclude routing for electrical leads of the coil and/or an electrodethat makes contact with the skin. The electrode may provide a means ofrecording electrical potential on the body surface, and/or forelectrical stimulation of the wearer.

Still other objects and advantages of the present invention will in partbe obvious and will in part be apparent from the specification.

The present invention accordingly comprises the features ofconstruction, combination of elements, and arrangement of parts all asexemplified in the constructions herein set forth, and the scope of theinvention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the inventive embodiments, reference ishad to the following description taken in connection with theaccompanying drawings in which:

FIG. 1 shows an exploded view of a prior art headphone set having axialshaker suspended on a spiral-cut spring;

FIG. 2A shows a perspective view of a prior art headphone illustratingan axial shaker orientation that stimulates the skin by plunging the earcup against the side of the head;

FIG. 2B shows a graph illustrating the excess bass audio apparentgenerated by the prior art headphones of FIG. 2A;

FIG. 3A shows a chart illustrating two physical bounds on the forceoutput of an electromagnetic vibration module arising from limitationson the space available for translating the mass and from the limitedforce output of the coil;

FIG. 3B shows a cross-sectional view of an exemplary module including anarrangement of a coil, magnets and a suspended inertial mass obeying theconstraints illustrated in FIG. 3A, in accordance with some embodiments;

FIG. 3C shows a cross-sectional view of the module of FIG. 3B withexemplary magnetic flux lines superimposed thereon, in accordance withsome embodiments;

FIG. 4A shows a perspective view of an exemplary damped planarelectromagnetic module, in accordance with various embodiments describedherein;

FIG. 4B shows an exploded view the module of FIG. 4A, in accordance withvarious embodiments described herein;

FIG. 5A shows an exploded view of an exemplary headphone showing theorientation of the module in the ear cup, in accordance with variousembodiments described herein;

FIG. 5B shows a perspective view of a user wearing the headphone of FIG.5A and illustrates how the motion axis lies parallel to the side of theuser's head, in accordance with various embodiments described herein;

FIG. 5C shows that the measured acceleration of the exemplary headphoneof FIG. 5A at various frequencies is approximately uniform over therange 40-200 Hz, in accordance with various embodiments describedherein;

FIG. 6A shows an exploded view of an exemplary suspension, in accordancewith various embodiments described herein;

FIG. 6B shows a detailed perspective view of a portion of the exemplarysuspension of FIG. 6A, in accordance with various embodiments describedherein;

FIG. 7 shows a perspective view of a portion of an exemplary module, inaccordance with various embodiments described herein;

FIG. 8A shows an exploded view of an exemplary torsional module, inaccordance with various embodiments described herein;

FIG. 8B shows a schematic view of the torsional module of FIG. 8Aillustrating the action its flexures, in accordance with variousembodiments described herein;

FIG. 8C shows a perspective view of a user wearing headphonesincorporating the torsional module of FIG. 8A and illustrates exemplaryrotational motion in a plane parallel to the side of the user's head, inaccordance with various embodiments described herein;

FIG. 9A shows an exploded view of an exemplary compliant vibrationmodule, in accordance with various embodiments described herein;

FIG. 9B shows a cross-sectional view of the compliant vibration moduleof FIG. 9A, in accordance with various embodiments described herein;

FIG. 10A shows an illustrative two-dimensional finite element analysisof a coil carrying a current in the magnetic gap formed by a singlemagnet and flux guides, in accordance with various embodiments describedherein;

FIG. 10B shows a perspective view of an exemplary module having multiplecylindrical coils in circular magnetic gaps driving magnets coupled toan inertial mass, in accordance with various embodiments describedherein;

FIG. 11 shows a perspective view of an exemplary elongated version ofthe coil and gap, driving an elongated magnet and mass, in accordancewith various embodiments described herein;

FIG. 12 shows a cross-sectional view of an exemplary housing withelements to guide the lateral translation of the mass and magnets asthey are driven by the coil(s) at one end, in accordance with variousembodiments described herein;

FIG. 13A shows a perspective view of an exemplary vibration module, inaccordance with various embodiments described herein;

FIG. 13B shows an exploded view of the module of FIG. 13A illustratingthe suspension and attachment to the housing, in accordance with variousembodiments described herein;

FIG. 14A shows a perspective view of an exemplary headphone ear cup withretaining features for a vibration module, in accordance with variousembodiments described herein;

FIG. 14B shows an exploded view of the headphone ear cup of FIG. 12A, inaccordance with various embodiments described herein;

FIG. 14C shows a perspective view of a user wearing headphones includingthe headphone ear cup of FIG. 12A, in accordance with variousembodiments described herein;

FIG. 15A shows a perspective view of a user wearing an exemplaryheadphone with multiple vibrating cushions situated on the headphone, inaccordance with various embodiments described herein;

FIG. 15B shows a cut-away cross-sectional view of a portion of theheadphone of FIG. 15A, in accordance with various embodiments describedherein;

FIG. 16A shows a perspective view of a user wearing an exemplaryheadphone with armatures that position vibrating elements, in accordancewith various embodiments described herein;

FIG. 16B shows an exploded view of the armatures of FIG. 16Aillustrating degrees of freedom afforded by an example of an armature,in accordance with various embodiments described herein;

FIG. 16C shows an exploded view of an exemplary positioner withvibration element and electrode, in accordance with various embodimentsdescribed herein; and

FIG. 17 shows a perspective view of another exemplary positioner, inaccordance with various embodiments described herein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Various embodiments for providing damped electromagnetically actuatedplanar motion for audio-frequency vibrations are disclosed herein.

The force output across a frequency range of a tactile transducer usedfor this purpose is limited by the space available for moving theinternal mass and the peak force of the actuator causing the movement.FIG. 3A shows chart 30 illustrating these two physical bounds on theforce output of an electromagnetic vibration module arising fromlimitations on the space available for translating the mass and from thelimited force output of the coil. For an electromagnetic actuator, theselimits may be termed travel limit 31 and coil limit 32, respectively. Ifthe system is not underdamped, the output of the transducer can bedescribed by a curve in region 33, below these limits 31 and 32.

The travel limit obeys the equation:

F _(max) =mx _(max)(2πf)²  (1)

where:

-   -   F_(max)=[N], maximum force    -   X_(max)=[m], space in package available for displacement    -   m=[kg], mass in motion    -   f=[Hz], frequency

FIG. 3B shows an exemplary vibration module 300 obeying the constraintsillustrated in FIG. 3A, in accordance with some embodiments. Inparticular, FIG. 3B illustrates how travel limit 31 and coil limit 32apply to embodiments of the present invention, which may generallyinclude moving mass 304, oppositely polarized magnets 302 a and 302 b(collectively oppositely polarized magnets 302), coil 307, flux guides,308, and housing 305.

In one particular example, travel limit 31 for vibration module 300 maybe calculated for moving mass 304 having a mass of 0.015 kg that canundergo a maximum displacement of ±0.002 m (x_(max)) before contactingthe wall of housing 305. In this example the product of mass andavailable displacement are (0.015 kg)-(0.002 m)=3E-5 kg·m. To maximizeforce, the product of mass and available travel should be maximized. Thehigher the frequency of interest, the greater the acceleration that ispossible, up to some limit imposed by the actuator. For anelectromagnetic actuator, this coil limit 32 typically reflects themaximum current I that can be put through the copper windings. There arealso an instantaneous limit associated with the power supply and alonger term limit-typically seconds to minutes-associated withoverheating the coil. In some embodiments, the mass times thedisplacement may be, for example, 1×10⁻⁵ kg-m or greater.

FIG. 3C illustrates the parameters that affect the coil limit. Inparticular, oppositely polarized magnets 302 produce a magnetic field Btransecting coil 307 formed from a wire of length 1 The Lorentz force Farising from the current transecting the magnetic field is:

F _(max) =i _(max) ∫d{right arrow over (l)}×{right arrow over (B)}   (2)

where:

F_(max)=[N], maximum force

i_(max)=[Amp], current limit of supply, or thermal limit

I=[m], wire length

B=[Tesla], magnetic field strength

Force output may be maximized by arranging coil 308, magnets 302, andflux guides 308 to steer maximum magnetic flux B through coil 307cross-section carrying current I, and to provide a low-resistance pathfor heat out of the coil so that current I_(max) does not produce anunacceptable temperature rise. For illustration, a practical coil limitof 1 N Force is assumed in FIG. 3A. Together the travel limit and coillimit define the maximum steady-state force output of a criticallydamped transducer.

FIGS. 4A and 4B show, respectively, a perspective and exploded view ofan exemplary damped planar electromagnetic vibration module (vibrationmodule 400), in accordance with various embodiments described herein. Insome embodiments, vibration module 400 may be generally flat or planarso that it can easily be incorporated into the ear cup of a headphone,and provide a reciprocating force along axis 401 orthogonal to thethinnest dimension of the vibration module.

As shown in FIG. 4B, a pair of oppositely polarized magnets 402 can beheld by a retainer 403 in a pocket or depression formed in mass 404,which may be suspended on flexures 406 within a frame or housing 405.Flexures 406 provide for movement of inertial mass 404 and magnets 402along axis 401, which may be orthogonal to the thinnest dimension of thevibration module. Lateral forces can be imparted to magnets 402 byvirtue of a Lorentz force generated by passing current through an coil407, which is depicted in FIG. 4B as an elongated coil of conductivewire. Upper flux guide 408, which may be a piece of iron, or othersuitable ferromagnetic material, adhered to or otherwise placed in closeproximity to coil 407, can guide the magnetic flux and act as a heatsink and means of retaining coil 407 in place within housing 405. Forexample, magnetic flux guide 408 can retain coil 407 in slot 409 formedin top plate 405 a of housing 405 so that coil 407 is fixed with respectto frame 405. In some embodiments, a portion of the housing (e.g. topplate 405 a in the embodiment depicted in FIG. 4) supporting the coil(e.g. coil 407) can be a printed circuit board with components toprovide low-pass filtering of an audio signal and/or power amplificationfor driving the coil.

In some embodiments, movement of the mass 404 and magnets 402 may bedamped by thin layer of viscous ferrofluid 410 retained in a gap betweenthe magnets 402 and bottom plate 405 b of housing 405. An additionallower magnetic flux guide 408 b may be provided to counterbalance theattractive force drawing magnets 402 toward upper flux guide 408 a.Current may be routed to coil 407 using conductive leads 407 a. In someembodiments conductive leads 407 a may be soldered to solder pads 405 aaformed on an accessible surface of housing 405 (e.g. a top surface oftop plate 405 a as shown in FIG. 4B or any other outer surface). Leadsfrom a power source (not shown) may also be attached to solder pads 405aa in order to electrically couple the power source to coil 407.

FIG. 5A shows an exploded view of exemplary headphone set 50illustrating the orientation of vibration module 500 in the ear cup, inaccordance with various embodiments described herein. Vibration module500 is depicted mounted so as to occupy relatively little of thethickness of ear cup 51 and to provide a reciprocating force in an axis501 substantially orthogonal to the thinnest dimension of the vibrationmodule. Vibration module 500 can be situated behind audio driver 52 andsound baffle 53, which may be mounted on the headphone bow 54. Providingvibration modules that generate damped electromagnetically actuatedplanar motion for audio-frequency vibrations can advantageously speed auser's reaction time by adding tactile sensations to audio provided bythe headphone set. The vibrations can also help to preserve the user'shearing by lowering the user's preferred acoustic listening level.

FIG. 5B shows a perspective view of a user wearing the headphone of FIG.5A and illustrates how the motion axis lies parallel to the side of theuser's head, in accordance with various embodiments described herein. Asshown in FIG. 5B, a time-varying voltage can produce forces andaccelerations in a plane parallel to the side of the headphone wearer'shead along axis 501 labeled “x,” though one skilled would appreciatethat the forces and accelerations directed along a different axis, suchas the axis labeled “y,” for example, lying substantially in the sameplane, may also be suitable for providing skin tractions that areperceptible as vibration while producing minimal excess sound.

FIG. 5C shows a chart 50 c of experimental results of the measuredacceleration of the exemplary headphone of FIG. 5A, in accordance withvarious embodiments described herein. In particular, chart 50 cdemonstrates that the measured acceleration of the ear cup along axis501 is substantially uniform over the range 40-200 Hz. To characterizethe frequency response, sinusoidal voltage (V_(vibrate)) ranging from 20to 200 Hz was applied to one of the conductive leads 55 attached to thecoil of vibration module 500 while the other lead was held at groundpotential (GND) as shown in FIG. 5A.

Below approximately 40 Hz, in sub-resonance frequencies 502, the outputof vibration module 500 is constrained by the “travel limit” (e.g.travel limit 31 of FIG. 3A) because as voltage is increased, the mass(e.g. mass 304 of FIG. 3B) travels farther, and increasing the voltagetoo high results in the travel exceeding x_(max) and causes the mass tocome into contact with the frame (e.g. housing 305 of FIG. 3B),producing an undesirable acoustic knocking sound. Above approximately 40Hz, the system response is constrained by the “coil limit” (e.g. coillimit 32 of FIG. 3A) where increasing the voltage eventually produced anundesirable increase in coil temperature. The viscosity and volume ofthe damping fluid (e.g. viscous ferrofluid 410 of FIG. 4B) in vibrationmodule 500 were adjusted to damp resonance that would be evident at30-50 Hz, to achieve the relatively uniform, non-peaked, responseevident in FIG. 5C between 40 and 200 Hz in range 503. The absence ofresonant peak in the response makes it possible to reproduce the tactilecomponent of a musical experience with previously unattainable highfidelity.

It will be evident to one skilled in the art that the embodiment of thevibration module presented in FIGS. 3A-4B is a particular, non-limitingexample, meant merely to illustrate an exemplary vibration module thatcould be employed in accordance with various embodiments of the presentinvention. Additional exemplary vibration module embodiments will now bepresented, each of which may be configured to produce appropriatelyoriented motion in a headphone as shown in FIGS. 5A-5C.

FIG. 6A shows an exploded view of vibration module 600, in accordancewith various embodiments described herein. Vibration module 600 issubstantially similar to vibration module 400, except that it isequipped with an alternative suspension system for accurately locatingand spacing the suspended mass within the housing. In particular,vibration module 600 includes mass 604 to which flexures 606 are bondedon opposite ends, so as to suspend the mass within housing 605. Flexures606 engage holes 605 ab and 605 bb in top plate 605 a and bottom plate605 b, respectively. The pocket in the mass 604 may be equipped withbottom 608, embodied in FIG. 6A as a thin plate bonded to the mass. Themagnet pair and portions of the housing are omitted in this instance forclarity.

FIG. 6B shows a detailed perspective view of a portion of flexure 606,in accordance with various embodiments described herein. Flexure 606 mayinclude projecting tabs 606 a that engage holes 605 ab and 605 bb in thetop and bottom plates, to provide alignment of the plates and set thesize of the gap between them. Flexures 606 may also have shoulders 606 bthat provide clearance for flexing member 606 c to prevent contactbetween of the flexing member 606 c and top plate 605 a and bottom plate605 b as mass 604 travels within housing 605.

FIG. 7 shows a perspective view of a portion of exemplary vibrationmodule 700, in accordance with various embodiments described herein.Vibration module 700 includes oppositely polarized magnets 702 coupledto (e.g. affixed with an adhesive to) suspension base member 711.Flexures 706 may be formed integrally with or otherwise coupled tosuspension base member 711. Mass 704 may be arranged and coupled tosuspension base member 711 (e.g. at an end of the suspension base member711 opposite magnets 702). In some embodiments, mass 704 may be orinclude a battery for powering vibration module 700. The portion ofvibration module 700 depicted in FIG. 7 may be enclosed in a housing,not shown (e.g. housing 405 of FIG. 4).

FIG. 8A shows an exploded view of exemplary torsional vibration module800, in accordance with various embodiments described herein. Vibrationmodule 800 is a rotational analog of the linearly traveling vibrationmodule examples disclosed thus far. As shown in FIG. 8A two pairs ofoppositely polarized magnets 802 and two inertial masses 804 may becoupled to a disk 812 suspended on flexures 806 that allow torsionalrotation of the disk about central hub 812 a. The ends of the hub may becoupled to front housing member 805 a and back housing member 805 b.Coils 807 can be retained in slots of front housing member 805 a andeither coupled to or brought into close proximity to magnetic fluxguides 808 a. Magnetic flux guides 808 b may also be provided on backhousing member 805 b.

FIG. 8B shows a schematic view of torsional vibration module 800illustrating the action of flexures 806, in accordance with variousembodiments described herein. In particular, FIG. 8B illustrates theaction of flexures 806 as they deflect from an initially straightposition 806-1 to a deflected position 806-2 as disk 812 rotates abouthub 812 a.

FIG. 8C shows a perspective view of a user wearing headphone set 80incorporating torsional vibration module 800 and illustrates exemplaryrotational motion in a plane parallel to the side of the user's head, inaccordance with various embodiments described herein. Rotation of themasses on central disk 812 produces counter rotation of the ear cupabout the axis of the hub along rotational path 801 labeled “a” Themotion lies in the plane parallel to the side of the user's head,producing skin tractions perceptible as vibration, without causing achange to the volume of air inside the ear cup, thus minimizing unwantedsound. This particular embodiment of the rotational system has twice thenumber of coils and magnets of the linear systems illustratedpreviously, but produces the same general effect. Accordingly, oneskilled in the art may appreciate that any number (N=1, 2, 3 . . . ) ofactuator elements can provide equivalent or similar results. Likewise,it should be apparent to one skilled in the particular shape of thesectors housing masses 804 and magnets 802 may be varied, such thatother shapes, such as half-circular sectors, can perform in anequivalent or similar manner to the explicitly disclosed embodiments.

Thus far, several rigid embodiments in accordance with the presentinvention have been disclosed. However, compliant constructions suitablefor direct skin contact are also contemplated as falling within thescope of the invention. FIG. 9A shows an exploded view of exemplarycompliant vibration module 900, in accordance with various embodimentsdescribed herein. Vibration module 900 can include a planar pair ofoppositely polarized magnets 902 embedded in a compliant puck 904supported on a layer of ferrofluid 911, where both puck 904 andferrofluid 911 are trapped between two impermeable elastic membranes.The compliant materials used in formation of compliant vibration module900 may have an elastic modulus of less than 50 MegaPascal.

Lower membrane 905 b provides a stationary platform for movement,whereas the upper membrane 905 a moves with the puck 904 and mayoptionally be corrugated to easily afford lateral movement of puck 904.The upper and lower membranes may be sealed at the circumference, forexample by a heat sealing process for thermoplastic elastomers, byadhesive or solvent bonding, or any other suitable bonding method. Asbefore, the magnets are urged laterally by current passed through coil907. In this embodiment, the coil 907 can be enclosed in a compliantstage 905 c so as to provide a supporting stage for movement of the puck904.

Applying time-varying signals to lead 907 a of coil 907 with respect tolead 907 b produces time-varying forces on the puck 904, andcorresponding lateral accelerations of upper membrane 905 b coupled toit. Upper membrane 905 b, in turn, may be placed in direct contact withthe wearer's skin or may be integrated with the cushion fabric incontact with a wearer's skin.

FIG. 9B shows a cross-sectional view of compliant vibration module 900,in accordance with various embodiments described herein. As illustratedin FIG. 9B, current I flows through coil 907, urging magnets 902laterally. Relative movement between the compliant upper membrane 905 aand stage 905 c is facilitated by the ferrofluid layer 911. The seal atthe circumference of vibration module 900 is evident where the lowermembrane 905 b contacts upper membrane 905 a.

Although examples so far have focused on vibration modules incorporatingplanar pairs of magnets, embodiments of the present invention are alsocontemplated having alternative arrangements between magnet and coil.Several exemplary embodiments are shown in FIGS. 10A-13.

FIG. 10A shows an illustrative two-dimensional finite element analysisof coil 1007 carrying a current in the magnetic gap formed by a singlemagnet 1002 and flux guides 1008, in accordance with various embodimentsdescribed herein. Magnet 1002 has magnetic flux that is guided bymagnetic flux guides 1008 through an air gap in which coil 1007 carriescurrent I The generated Lorentz force urges coil 1007 in direction 1001a and the rest of the components illustrated in FIG. 10 in direction1001 b, opposing direction 1001 a.

FIG. 10B shows a perspective view of exemplary vibration module 1000, inaccordance with various embodiments described herein. Vibration module100 can include multiple drivers including cylindrical coils in circularmagnetic gaps driving magnets coupled to an inertial mass 1004. In someembodiments, one or more of these drivers may be situated along one edgeof mass 1004, so that applying time varying voltage to coils 1007generates Lorentz force on the magnets 1002 and flux guides 1008 andthereby urges mass 1004 to move along axis 1001 lying substantially inthe plane of the vibration module. If coils 1007 are fixed to a housing(omitted for visual clarity) the magnets, flux guide, and inertial masstranslate with respect to the housing.

FIG. 11 shows a perspective view of exemplary vibration module 1100having a coil and gap structure that is integral and elongated withrespect to the coil and gap structures of vibration module 1000, drivingan elongated magnet 1102 and mass 1104, in accordance with variousembodiments described herein. The resulting geometry uses an elongatedoval coil 1107 arranged in the air gap of an elongated flux guide 1108.As with the previously disclosed embodiments, time-varying voltagesweeping current through coil 1107 urges the magnet, flux-guide, andinertial mass laterally along an axis 1101 in the plane of the module.

FIG. 12 shows a cross-sectional view of an exemplary housing 1205 withelements 1206 that guide the lateral translation of mass 1204 andmagnets 1202 as they are driven by the coil(s) 1207 at one end, inaccordance with various embodiments described herein. Housing 1205 maybe a suitable housing for vibration modules 1000 and 1100 illustrated inFIGS. 10B and 11. Coil 1207 may be fixed to a wall of housing 1205. Whencurrent is passed through coil 1207, magnet 1202, flux guide 1208, andinertial mass 1204 are urged laterally along axis 1201 that lies in theplane of the vibration module. In this embodiment, the movement ofinertial mass 1204 can, for example, be guided by linear glides 1206rather than flexures. However, a person of skill in the art wouldrecognize that a variety of suspensions lie within the scope of thepresent invention, and that comparable results may be achieved withflexures, a ferrofluid, bushings, and even ball bearings provided thatthey are pre-loaded and packed with viscous grease so as not to rattleaudibly when reciprocated at frequencies in the 20-200 Hz range.

FIG. 13A shows a perspective view of yet another exemplary vibrationmodule 1300, in accordance with various embodiments described herein.Vibration module 1300 includes thin magnet 1302 polarized along the thinaxis. It operates in the center of a long coil with an oval crosssection 1307. The flat sides of the oval carry current I runningtransverse to the flux of magnet 1302, and therefore generates a forceperpendicular to both the current and the magnetic flux. That is, theLorentz force urges magnet 1302 in a direction aligned with its longaxis 1301, and urges coil 1307 in the opposite direction. Magnetic fluxguide 1308 provided concentrically outside coil 1307 can improveorientation of the magnetic flux. Bracket 1303 can couple movement ofmagnet 1302 to inertial mass 1304.

FIG. 13B shows an exploded view of vibration module 1300 illustrating anexemplary suspension and attachment to housing 1305, in accordance withvarious embodiments described herein. Flexures 1306 can be attached toinertial mass 1304 so that inertial mass 1304 may move with respect tohousing 1305. In some embodiments, housing may be provided with matingsurface 1305 a that maybe coupled to magnetic flux guide 1308 providedaround coil 1307 so that coil 1307 is fixed with respect to the housing.A second bracket 1303 b for translating the motion of magnet 1302 toinertial mass 1304 is shown. Also shown is the axis of motion 1301 ofinertial mass 1304.

FIG. 14A shows a perspective view of an exemplary headphone ear cup 141with retaining features 142 for holding a vibration module, inaccordance with various embodiments described herein. Although clips aredepicted in FIG. 14A, other suitable retaining features, such asadhesives and fasteners, for example, may be substituted.

FIG. 14B shows an exploded view of the headphone ear cup 141, inaccordance with various embodiments described herein. In particular,FIG. 14B depicts an embodiments of the present invention in whichmovement of the inertial mass is visible through a wall of headphone earcup 141. In this embodiment, the back plate 1405 of the vibration module1400, is formed from a transparent material, such as glass ortransparent plastic, for example, and headphone ear cup 141 is providedtransparent window 141 a. Together, back plate 1405 and transparentwindow 141 a afford a view of the moving inertial mass 1404

FIG. 14C shows a perspective view of a user wearing headphone set 140,including headphone ear cup 141, in accordance with various embodimentsdescribed herein. As shown in FIG. 14C the edges of window 141 a, onwhich a visual design 141 b is optionally displayed, the movement ofinertial mass 1404 and/or other components of vibration module 1400 arevisible. That is, a viewer may be provided a clear optical path so thatvibration of vibration module 1400 within ear cup 141 is visible whenthe vibration module is worn on a user's head.

FIG. 15A shows a perspective view of a user wearing an exemplaryheadphone set 150 with multiple vibrating cushions 152, in accordancewith various embodiments described herein. In particular, vibratingcushions 152 are provided on headphone bow 153 to produce tangentialtractions on the wearer's skin at multiple locations.

FIG. 15B shows a cut-away cross-sectional view of a portion of headphoneset 150, in accordance with various embodiments described herein. FIG.15B illustrates headphone bow 153 and a compliant vibration module 1500,which may be similar to compliant vibration module 900 of FIGS. 9A and9B, embedded in a cushion formed from foam member 154 and cover 155. Thecushion may be attached (e.g. with adhesive 156) to headphone bow 153.In this embodiment, the movement of the compliant puck within vibrationmodule 1500 causes shear movement 1501 of the cushion cover where itrests on the wearer's skin or hair.

FIG. 16A shows a perspective view of a user wearing an exemplaryheadphone set 160 with armatures 166 that position vibrating elements162, in accordance with various embodiments described herein. As shownin FIG. 16A, one or more positioners 166 may be provided to adjust thelocations of the vibrating elements 162 with respect to headphone bow164 and ear cup 161, so as to provide vibrations at various locations onthe wearer's skin.

FIG. 16B shows an exploded view of armatures 166 of FIG. 16Aillustrating degrees of freedom afforded by an example of an armature,in accordance with various embodiments described herein. Here, avibrating element, such as compliant vibration module 1600 (which may besimilar or identical to compliant vibration module 900 of FIGS. 9A and9B), is positioned so as to impose tangential shear tractions on thewearer's skin. The vibration axis may be chosen to lie primarilyparallel to the user's sagittal plane (that is parallel with, but notnecessarily coincident with the side of the user's head), to minimizeunwanted movement toward and away from the user's ear, to minimizeunwanted sound.

As further shown in FIG. 16B, armature 166 may provide a surface 166 athat supports vibration module 1600 and also affords lateral movement1601 over the surface of the user's skin, for example by rotation 1601 aabout a rotational degree of freedom provided by a pivoting base 166 b.Armature 166 can also provide rotation 1601 b about a second degree offreedom by virtue of a hinged connection 166 c between armature 166 andarmature base 166 b that allows movement that accommodates the variableheight of the user's skin with respect to the positioner base 16 b whereit connects to headphone 160.

FIG. 16C shows an exploded view of positioner 166, in accordance withvarious embodiments described herein. In particular, FIG. 16Cillustrates how electrical leads for the vibrating element 1600 may berouted through it, and how it affords a mounting point and electricalconnection 166 d for an optional skin-contact electrode 166 e. Electrode166 e may, through an independent electrical lead 166 f source or sinkcurrent independent of any time-varying voltage applied to the lead 166g of the vibrating element.

The skin contact electrode thereby provides a means of stimulating thewearer, for example to provide transcranial direct current stimulation.Because vibration masks pain, the pain commonly associated withelectrical stimulation through the skin can be avoided. The electrodecan also provide a one or more sensors for recording electricalpotentials on the surface of the wearer's body, for example signalsarising from the wearer's electroencephalogram, indicating brainactivity, or the electrooculogram, indicating eye orientation, or thewearer's electromyogram indicating contraction of the facial muscles,the conductivity of the user's skin, indicating sweating, or any otherelectrical potentials on the surface of the wearer's body.

FIG. 17 shows a perspective view of another exemplary positioner 176, inaccordance with various embodiments described herein. Positioner 176 canhave an extensional degree of freedom 1701 that affords radialpositioning of the skin contact point with respect to the positionerbase 176 b. Additional flexibility is optionally imparted to theorientation of the skin contact point by elastic pillars 176 g that jointhe support for the vibrating element to the positioner. It is clear toone skilled in the art that these various degrees of freedom in thepositioner may be passive, spring loaded, or electromechanicallyactuated to provide a massaging motion by positioning a vibration moduleover a desired location on a user's body.

It should be understood that the aspects, features and advantages madeapparent from the foregoing are efficiently attained and, since certainchanges may be made in the disclosed inventive embodiments withoutdeparting from the spirit and scope of the invention, it is intendedthat all matter contained herein shall be interpreted as illustrativeand not in a limiting sense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed, and all statements of the scope of the invention that, as amatter of language, might be said to fall there between.

What is claimed is:
 1. An apparatus for imparting motion to the skin ofa user, the apparatus comprising: a housing; a plurality of coilscapable of carrying electrical current; a plurality of magnets arrangedin operative proximity to the plurality of coils; a moving portioncomprising an inertial mass and the plurality of magnets; a suspensioncomprising a plurality of flexures that guides the moving portion in aplanar motion with respect to the housing and the plurality ofconductive coils; wherein movement of the moving portion is damped by aferrofluid in physical contact with at least the moving portion; andwherein the ferrofluid reduces at least a mechanical resonance withinthe frequency range of 40-200 Hz in response to electrical signalsapplied to the plurality of conductive coils.
 2. The apparatus of claim1 wherein said housing is generally cuboid in shape.
 3. The apparatus ofclaim 2 wherein the cuboid-shaped housing has a thickness less thanone-third of the width, where the thickness and width are bothorthogonal to the direction of motion of the moving portion, and thethickness is less than the width.
 4. The apparatus of claim 2 whereinthe cuboid-shaped housing has a length dimension in the direction ofmotion of the moving portion, and a thickness dimension perpendicular tothe length dimension, wherein the thickness dimension is less thanone-third of the length dimension, and the thickness is less than thewidth.
 5. The apparatus of claim 1 wherein said housing comprises atleast one magnetic flux guide comprising a ferromagnetic material. 6.The apparatus of claim 1 wherein said housing comprises a plurality ofmagnetic flux guides, each comprising an upper magnetic flux guide and alower magnetic flux guide.
 7. The apparatus of claim 4 wherein saidmagnetic flux guide comprises a portion of said housing and is coupledto at least a coil.
 8. The apparatus of claim 5 wherein each saidmagnetic flux guide is coupled to a plurality of coils.
 9. The apparatusof claim 1 wherein each of said plurality of coils is an elongated ovalwith substantially flat sides.
 10. The apparatus of claim 1 wherein thelong axis of each of the plurality of flexures is substantially in theplane of the moving portion.
 11. The apparatus of claim 9 wherein eachof said flexures is thinner along the motion axis of the moving portionthan it is in directions orthogonal to the motion axis of the movingpart.
 12. The apparatus of claim 9 wherein each of said flexures is moreresistant to motion transverse to the plane of the moving portion thanit is to linear motion in the plane of and along the motion axis of themoving portion.
 13. The apparatus of claim 1 wherein said apparatus iscapable of producing audio frequency vibrations in response toelectrical signals applied to the plurality of coils.
 14. The apparatusof claim 1 wherein each of said plurality of magnets is mounted so thatit has a polarity that is the opposite of the polarity of the magnet ormagnets adjacent to it.
 15. The apparatus of claim 1 wherein saidflexures are not integrally formed with said moving part or saidhousing.
 16. The apparatus of claim 1 wherein said moving portion movesrelative to said plurality of coils along a plane that is orthogonal tothe thickness dimension of the housing, wherein said thickness dimensionis smaller than the length dimension and the width dimension.
 17. Anapparatus for imparting motion to the skin of a user, the apparatuscomprising: a housing or frame; a conductive coil capable of carryingelectrical current; a plurality of magnets arranged in operativeproximity to the plurality of coils; a moving portion comprising aninertial mass and the plurality of magnets; a suspension comprising aplurality of flexures that guides the moving portion in a planar motionwith respect to the housing and the plurality of conductive cons;wherein movement of the moving portion is damped by a ferrofluid inphysical contact with at least the moving portion; and wherein theferrofluid reduces at least a mechanical resonance within the frequencyrange of 40-200 Hz in response to electrical signals applied to theplurality of conductive coils.
 18. The apparatus of claim 17 wherein thehousing or frame has a thickness less than one-third of the width, wherethe thickness and width are both orthogonal to the direction of motionof the moving portion.
 19. The apparatus of claim 17 wherein each ofsaid plurality of coils is an elongated oval with substantially flatsides.
 20. An apparatus for generating damped electromagneticallyactuated planar motion, the apparatus comprising at least one vibrationmodule, said vibration module comprising: a housing; a coil capable ofcarrying electrical current; a plurality of magnets arranged inoperative proximity to the plurality of coils; a moving portioncomprising an inertial mass and the plurality of magnets; a suspensioncomprising a plurality of flexures that guides the moving portion in aplanar motion with respect to the housing and the plurality ofconductive coils; wherein movement of the moving portion is damped by aferrofluid in physical contact with at least the moving portion; andwherein the ferrofluid reduces the Q-Factor of the response of theapparatus over at least a portion of the frequency range of 40-200 Hz inresponse to signals applied to the plurality of conductive coils. 21.The apparatus of claim 20 wherein: the apparatus comprises a headphoneset, said headphone set comprising a headphone bow with ear cups atopposite ends; the at least one vibration module is coupled to at leastone of the headphone bow or ear cups; and the at least one vibrationmodule guides motion of the moving portion in a plane substantiallyparallel to the surface of the user's head contacted by at least one ofsaid headphone bow and said ear cups.